Tracer with power-driven steerable traction wheel



Feb.. l5, 1949. N. E. .ANDERSON 2,46%585 TRACER WITH POWER-DRIVEN STEERABLE TRACTION WHEEL Filed May 22, 1947 2 sheets-sheet 1 a. c l S A F a N www [x G 8 M/O\ .|J w Il I L? fumi o G .c M 5 ,6 u m., 2 2 8 u N\\ |M/ fl H f. H 'I Hr I l 1 l O 2 x 7\ 4 ma 2 7 www/Mum |J,/- m fr f F \\l l I I l I Illw IIIIIII L "0 `\,\..l/M\ 4 Feb. 15, 1949. E, ANDERSON 2,461,585

TRACER WITH POWER-DRIVEN STEERABLE TRA'cTIoN WHEEL4 Filed May 22, 1947 FIG.4 FIG.5

2 Sheets-Sheet 2 L, INVENTO masa/f f. ,4f/msm y.; Zim? ATTORNEYS N Patented Feb. 15, 1949 TRACER WITH POWER-DRIVEN STEERABLE TRACTION WHEEL Nelson E. Anderson, Scotch llains, J., assignor to Air Reduction -Com corporation of New Yor pany, Incorporated, a k

Application May 22, 1947, Serial No. 749,810 11 Claims. (C1. Z50-41.5)

This invention relates to apparatus of the type that is propelled and steered by a power-drivensteerable traction wheel. More particularly the invention relates to power-driven steerable tracers for guiding the course of an instrumentality, such as a welding or cutting torch, in accordance with a drawing or pattern Tracers of this kind are commonly used on universal cutting or welding machines such as those of the pantograph type in which a gas cutting 3 or welding torch is mounted on one part of a pantograph structure, such as the front bar of a folding parallelogram frame, and the tracer is mounted on another part so that the torch is capable of universal movement in a plane and so that when the tracer is caused to follow the outline of the pattern the torch will be guided accordingly.

One type of tracer for use in this way comprises a traction wheel that rolls on the surface containing the pattern. The traction wheel is powerdriven at constant speed by an electric motor through a drive shaft the aXis of which intersects the axis about which the traction wheel rotates. The traction wheel is rotated from the drive shaft by suitable reduction gearing. The axle of the traction wheel is journalled in a sleeve or other member which is rotatable about the axis oi the drive shaft. By rotating this member the traction wheel can `be steered so-that some point on the tracer used as a reference point, or pattern-tracing point, can be made to follow the outline of the pattern.

The traction wheel is usually steered by hand,

but recently an electronic tracer has come into use in which the traction wheel is automatically steered to cause the tracer to follow the outline of the pattern. The electronic tracer has means for Vprojecting a beam of light on the line for-ming the pattern and the light is reiiected into a photoelectric cell in the tracer. The variation in the .amount of light.received by the photo-electric cell if the tracer deviates too far from the course it is supposed to follow causes the steering mechanism to steer the traction wheel so as to bring the tracer back onto its proper course.

In all previous power-driven tracers of the kind above described in which the drive motor is stationary with respect to the frame of the device, the steering of the traction wheel, whether done manually` or automatically, iniiuences the speed of rotation of the traction wheel. This is undesirable when the instrumentality moved by the tracer should travelat some selecteduniform speed as in the case of an oxygen cutting-torch,

traced by the tracer.

because when the tracer is turning a cornerl the tracer and hence the torch or other instrumentality are caused to travel faster or slower than the desired speed. Moreover, the driving of the traction wheel from the drive shaft produces a torque which tends to impart rotation to the member in which the traction wheel is journalled and hence tends to steer the traction wheel. This is especially undesirable when the traction wheel is automatically steered, as in an electronic tracer,

because any steering torque produced by the driving mechanism biases the automatic steering mechanism.

- The principal object of this invention is to provide a tracer or other apparatus having a powerdriven steerable traction wheel of the kind above described in which the desired ra-te of speed at which the apparatus is propelled by the traction wheel is not influenced by the steering of the traction wheel. f

Another object is to provide a tracer or other apparatus having a power-driven steerable traction wheel of the kind above described, in which the steering torque imparted to the traction wheel assembly by the driving mechanism is counteracted or nullifled so that it does not affeet the intentional steering of the traction wheel. A further object is ,to provide a power-driven automatically steered tracer, such as-`a tracer of the electronic type, in which the steering torque imparted to the tractionwheel assembly by the driving mechanism is counteracted or nullifled `so that it does not bias the automatic steering mechanism. y

The invention is illustrated in the accompanying drawings, in which:

f Figure 1 is a vertical section through the lower portion of the traction wheel assembly of a powerdriven tracer of the prior art;

Fig. 2 is a side elevation of an electronic tracer embodying the invention, shown in vertical section;'

Fig. 3 isan enlarged vertical section taken on the line 3-3 of Fig. 2;

Figs. 4, 5 and 6 are explanatory diagrams illustrating the principle of operation of the invention; l

Fig. 7 is a vertical section through the lower portion of a modified form of traction wheel assembly embodying the invention; and

Fig. 8 is a front elevation of the traction wheel assembly shown in Fig. 7.

certain parts being To give a correct understanding of how the steering of the tractionwheel of a power-driven tracer has heretofore had an undesirable elect on the speed of rotation of the traction Wheel, and how the driving of the traction wheel produces an objectionable steering torque, the prior art type of drive for the traction wheel has been illustrated in Fig. 1 and will first be described.

`Referring to this ligure, a portion of the main bevel pinion I6 on the lowerencll of'a stub; shafty I1 mounted to rotate in the member I2. A spur gear I8 connected to the upperfend.otthestub shaft I7 meshes with a spurgear` If9= fastened( to the lower end of the drive shaft 29. The drive shaft is driven at a constant speed! from-a motor (not shown) which is secured directly or indirectly to the frame II. The axis of the drivefshaft- 2B intersects the axis of the, traction wheel axle i4, and the peint of contact `of the traction wheel with the.- surface. along which the wheel rolls is: irrlinefwith the axis of the drivey shaft. The member |2v isfy rotatable about the axis ot the drive shaft and when so rotated changes, the orientation; or; direction of travell of the, traction. Wheel. Ina hand steered tracer thefmember' t2 is rotated manually to cause a given pattern-tracingJ point on theftracer (usually the-lower ende of a pointer which@ is-located alongside of the traction.` wheel whichy points approximately tov the place wherethetractionzwheel makes-contact with the surface along which it rolls) to follow the outline ot the pattern.v` In- .anl automatically steered tranensuclr asa tracerfof'theelectronic type, the er mein-ber :2g isrotatedg by anelectric motor controlled., automaticallyin they normal operation Voli theztracer but which can also be controlled whendesired by? a handnoperated; switch, as will later appear.

Tjoiprfopelthe i'fl'acer the shaft. 2,!)l is;` driven and rotates. the traction wheel` I3 through the gear train shown; llllrenz the member I-2 is rotated:

about the axis of the drive shaft 2llgto turn theI tractionwheelfassembly and change the direction oilv travelv otthe tracer.; the i driven. spur;v gear4r I8, beingwcarried by: the member I-2.f, revolves in a. planetary fashionfabout thef driving spur gear I9 on4 the drive shaft.Y This: planetary actionoi. theygearingL addettoon subtracts; from the rotation offthestub shaft I 'I and the; traction wheelv depending uponthe direction in which'` theA member trsgtumed.. Thuadurine the timethedirecn tion of travel of the tracer is; being varied.. as when, the 4tractionv wheel assembly is being turned to cause the patternrtracingwpointon the; tracer to` tracef anr arc.- cr a. completecrcle, the linear speedl of sucl'rpoint isncreased or decreased by the amount of rotationl added:l tov or subtracted frQIrlA .the .f tractionl Wheel; by the; planetary. action off the gearing. the tracer is used for moving and guiding an oxygen; cuttinggtorch thisY de y parturein speedfrorn-the desired speed atiwhich it moves when the tracer is; moving along a straight.` line-may., result inf losing; the; cut or in increasing the Widthof.- the korf.

It will also be seen from Fig. 1 that the gear 19.?

fil

infdrivinggthefgear.- I8toprope1; the tracer exerts aifolrce wllich acts-atlradiusRffto; produce a steering torquef-thatgtendsrto turn the-tract-ion` Wheel assembly about thefl axis: ccf-vy the drive shaft and change the direction of travel of the traction.;

wheel., YThis. steeringtorque is'objectionable-because-dt.. affects the. intentional. steering off-the traction Wheel. `It can affect the steering;` of the itraction wheel and make it more difficult to steer even when the traction Wheel is steered manually, but it is particularly objectionable in an automatically steered tracer because of the resulting bias on the automatic steering mechamsm. l

The speeding:V upg and slowing down, of; the traction. wheel by the above-mentionedI planetary action of the gearing during the time the direction of travel of the traction wheel is being varied, and.` the. steeringtorque produced by the driving mechanism, are inherent in all previous powerdriven tracers, in which the drive motor is stationary with respect to the frame, regardless of the'type: of gearing between the drive shaft and the-*traction wheel.

Figs.` 2 and Sillustrate an electronic tracer embodying the invention that is propelled at a constant speed: along all portions of the pattern even Whenrounding a ccrnem and in which the steeringtorque; produced by thedriving mechanism is counteracted so that it does notv -biasv the auto-V 24. Thesevrollers haveaxles secured toa plate 25` to which-theframe 26 of the electronic. tracer isattached.

Supported by the frame 2-6 is: an electric drive motorl 21 which rotates adrive shaft 28-through reduction gearinglrzll. I-he-motorZ-'I` has aspeed controlgovernor (not shown) which can beadjusted' so that the drivel shaft. 28.A is rotatedx at'. a

desired constant speed. A tachometerfis refsponsive tothe-rotationatspeed,of thedrive shaft 2,8.. and givesl a visual indication of the. speed. of travel of the tracer.

'lllhedrive shaft 28f-is mounted to.. rotate in ar sleeve 3.I which in- `turnfis rotatable about ther axis of thedrive shaft in bearlngs32 and 33. The

, lower, endcfthe sleevel isconnectedto a bifurcated member. Sli-between the two arms. ofi which the tractionwheel 35 and itsy associated mechanism are positioned..

Referringfnow to Fig. 3, which is anenlarged sectional4 view taken ontheline 3.-3. of Fig.2, there. is secured to the lower end.;of the drive shaft. 28. a bevel` pinion 36. which meshes with. a bevel gear 31. The gear 3.1. isrigdly securedto. the traction Wheel. 35, by screws 33. The

traction wheelandthe bevel gear 31. are mounted. onan axle. 39 that. is-.journalled in the two arms.

of, the. bifurcated-f member 3d. Thus.. the shaft 2B. rotates.A the. tractionv Wheel 35 through the bevel gearing 36.-.-31 ata' predetermined. desired speed; when. the traction wheel is, traveling in:

a. straight line.

By. rotating. thesleeve 3 tiarenough the angular. positionk ofV the traction wheel 35 may be varied through. 360.. one directionv or the other to steer. the traction wheel by meansof a. reversiblev electric motor dit The steering motor rotates a shaft M carrying awormY 42. which meshes'witha wormA Wheel 43. fastened to.r they sleevev 3|. Ar light source represented atl-.4d is located within the housing.y A beam: off light. represented by of. thetracer. the line his. projected. through the bottom of the housing ontofthefline of. thefpattern andy isf reflected` back intowaphoto-electricfcell repre*- z sented; atv 45.- The .steering motor 4ll-responds- The sleeve is rotated in tov changes in the.iamount 'of lightv received by the photo-electric cell from the pattern'line and rotates the sleeve 31' in one direction or the other tosteer the traction wheel and thereby cause thetracer to follow the line of the pattern in a manner well understood in the art. Switch means (not shown) may be provided for disconnecting thev steering motor from its automatic steering control circuit and connecting it to a handoperatedmomentary con-tact switch by means ofV which the steering motor can be controlled m-anually when desiredV to steer the traction wheel. y

In an electronic tracerit is the spot of projected light that follows directly on the pattern line but, of course, every point on the tracer housing Will move in a path having the same shape and size as the pattern. While the traction wheel isl automatically steered to cause the spot of light to follow the line oi the pattern, the traction wheel itself may be moving along a path which does not necessarily coincide with ythe pattern.

According to the invention the traction wheel is positioned so that its point of contact with the surface along which it rolls is located, not in line with the axis of the drive shaft as heretofore, but to one shaft as shown in Fig. 3. tween the drive shaft and are arranged as shown in wheel should be located on drive shaft is viewed in this son that will later appear. Now, assuming for the purpose of explanation and to contrast the operation of a tracer having an offset traction Wheel of the kind shown in Fig. 3 with the operation of previous tracers of the kind shown in Fig.v 1, that the pattern-tracing point is located in line with the axis of the drive shaft, itvvwill be seen from`Fig. 3 that if the drive shaft is rotated in the direction of the arrow the traction wheel will be rotated in a direction such that the tracer will be propelled away from the reader. If the sleeve in which the traction wheel is journalled is turned from left to right to steer the traction wheel so that the tracer will make a righthand` turn, the direction of movement of the sleeve and the direction in which the gear kSv'l revolves in a planetary fashion about the gear 36 will be in a direction opposite to that in which the drive shaft is rotating and the planetary action of the gearing will cause the traction wheel to speed up. However, it will be seen from Fig. 4, in which the solid line represents the portion of the pattern traced by the axis of the drive shaft and the dotted line represents the path followed by the traction wheel, that when the sleeve is turned to steer the traction wheel the traction wheel travels along an arc A which lies outside of and is longer than the arc B traced by the axis of the drive shaft. The longer distance through which the traction wheel is caused to travel while the axis of the drive shaft is traversing its arc at least partly compensates for the speeding up of the traction wheel caused by the planetary. action of the gearing, thereby making the rate of speed at which the axis of the drive shaft traverses the arc B to more nearly conform to the rate of speed at which it traverses the straight-line portions of the pattern.

Fig. 5 shows the of the drive shaft when the traction When the gears bethe traction wheel Fig. 3, the traction the left side of the figure, for the reapaths followed by the axis and by the traction wheel wheel is steered to cause the side of the axis of the drive tracer to maire'V a lefthand.. tum under the same conditions as previously-described, i. e., when the drive` shaft vis rotating in` thefdirection of the arrow shown in Fig. 3. Thesleevefin'. which the traction wheel is journalled is now turnedfromv right to left, i. e. in the same direction in which the drive shaft is rotating. The planetaryaction of the gearing will then slow down the rotation ofthe. traction. wheel, but it will be seen 'from Fig. 5v that the arc A followed by. the traction wheel is now inside'the arc B traced by the axis of the drive shaft: and the shorter path which the traction Wheel is caused. to fol-` low during the time that the axis of the drive shaft is traversing its arc at least partly compensates` for5 theslowing'down of the traction WheelcauSed by 'the planetary action of the gearing.

Even if the drive shaft rotates in a direction opposite to that indicated byv the arrow in Fig. 3 the tracer willl operate in thesarne 'way as just described but tl1e'-traction` wheel and the tracer will then, of course, travel' ina direction opposite to that indicated bythe arrows in Figs. 4 and 5'.

The traction Wheel should be positioned on that side of' the drive shaft vsuch that rotation tation of the traction. Wheel` yca uses the traction wheel to` travel in an arc which is outside the arc traced byY the axis. of the drive shaft and such that rotation of such member in a direction that slows down thev rotation of the traction wheel causes the traction wheel to travel in an are which; isfi'nside the; arev traced byy the axisy of the drive shaft.

While any amount of offset of the traction wheel with respect tothe axis off'the drive shaft a certain limit willillefbenecial by producing some compensating action for the change in speed of rotation of the traction wheel brought about by the planetary action,y of the gearing when the traction wheel assembly is turned to steer the traction wheeLHexact compensation can be obtained by offsetting the traction wheel from the axis of the drive.. shaft-a distance. such that the ratio fof the traction wheel radius to'such distance is equal to the reduction ratio of the gearing, as will now be'shown.

If C represents the circumference ofthe trac--y tion wheel its radiusl is upon the direction in which the sleeve is turned.

is, a complete circle, and `if the direction 1n which :itis turned during the tracing of the circle is such as to cause the planetary action of the gearing to add to lthe speed at which the traction wheel is driven by the drive shaft, then the one revolution of the sleeve that is required tosteer the tractic cause Ithe lpattern-tracing. point onthe tracerl to trace the complete pattern circle will advance a wheel inta circle and thereby circumference of the circle.

point on the circumference of the traction wheel one-third .the circumference of the traction wheel, or C/S. This amount of rotation of the traction wheel is added, to its notation by the drive shaft and results in speeding up the travel ofthe traction wheel, so that whereas it would take a certain interval of time for the patterntracing point on the tracer totrace the pattern circleii there were no planetary action of the gearing, the circle is now traced in a shorter interval of time due to the speeding up of the traction wheel by the planetary action of the gearing. To ycause the pattern-tracing point on the tracer to trace the pattern circle in the same interval of time in both cases, the path traveled by the traction Wheel during the time that it, is causing the pattern-tracingrpoint to trace the circle must be lengthened by the amount that the traction wheel is rotated circumferentially by the planetary action of the gearing, i. e. the traction wheel must be caused to travel along a circle which is C/3 longer in oirt'umference than the circle traced by the pattern-tracing. point. Therefore, the traction wheel must be offset with respect to the axis of the drive shaft by a distance such that the additional path C/3 is accounted for in one bodily revolution of the traction wheel about the axis of the drive shaft'which occurs when the sleeve 3| is rotated through one revolution to steer the traction Wheel in a cornplete circle. This additional path is equivalent to a circle whose circumference is C/S in length and which would be followed by the traction wheel if the sleeve 3l were rotated through one revolution about the axis of the drive shaft while the drive shaft is not rotating and has no translation. The radius of such a circle is the amount of offset that must be given to the traction wheel, and from the equation it will be seen that r= 611' The radius of the tractionwheel is as above stated, and hence the ratio oi the traction wheel radius to the offset distance of the traction wheel is 3 to lthe same as the reduction ratio of the gearing.

Taking a specific example, and still assuming that the gear reduction ratio is 3 to 1, let it be assumed that the circumference of the traction wheel is 6 inches and that a pattern is to be traced in the form of the complete circle P shown in Fig. 6 having a 6 inch circumference. Also, to simplify the explanation it will be assumed that the pattern-tracing point is in line with the axis of the drive shaft, although it might be any other point on the tracer, as previously stated. If a prior art tracer ofthe kind shown in Fig. l were used to trace such a circle, and if there were no planetary action of the gearing which speeds up or slows down the rotation of the traction wheel, three revolutions of the drive shaft would cause the traction wheel to traverse the complete Assuming that the desired linear speed of the cutting torch or other instrumentality moved bythe tracer is such as to call for a setting of the motor governor that will produce one revolution` of the drive shaft 28 8 in l'seconds, the'circle wouldbe traced in 30 seconds and this may be taken as the time in which the pattern circle should be traced to cause the linear speed of the tracer, and the instrumentality moved by it, to be the same when tracing an arc or circle as when moving in a straight line. Because of the planetary action I of the gearing, however, one complete revolution the offset distance is B to 1, or the same as the desired time in which the axis of r tion. The radius of the circle T of the sleeve 3l will cause the traction wheel to advance a circumferential distance of 2 inches. Therefore, the entire 6 inch circle will have been traversed by the traction wheelin two revolutions of the drive shaft (or 20 seconds) since this much turning of the drive shaft will account for the remaining circumferential distance of 4 inches travelled by the traction wheel. The traction wheel must therefore be offset with respect to the axis of the drive shaft a distance such that the traction wheel will then travel in a circle T whose crcuference is 2 inches longer than the 6 inch circle P traced by the axis of the drive shaft and this circle will then be traversed by the traction wheel in three revolutions of the drive shaft, or 30 seconds, which, as above` stated, is the drive shaft should trace the pattern circle P. The additional 2 inch path that the traction wheel is caused to traverse by its offset relation to the drive shaft axis in one revolution of the sleeve 3l is equivalent to a circle T' (Fig. 6) whose circumference is 2 inches in length and that would be traversed by the traction wheel in one revolution of the sleeve about the axis of the drive shaft if the drive shaft is not rotated and has no transladerived from the equation-circumference 2m' is 2'1r 'rr and is the amount of offset that should be given to thetraction wheel. The radius of the traction wheel itself is hence, the ratio of the traction wheel radius to the gear reduction ratio.

Regardless of the size of the traction wheel it is only necessary in all cases to divide its radius by the gear reduction ratio in order to determine the amount of offset that should be given the traction wheel in order to produce the results above described.

Similar reasoning will show that when the ratio of the traction wheel radius to the offset distance of the traction wheel is equal to the gear reduction ratio, and when the tracer is steered to make a turn of the kind shown in Fig. 5 the path of travel of the traction wheel is lessened by the proper amount to compensate for the slowing down of the rotation of the traction wheel caused by the planetary action of the gearing.

When the gearing is of the type shown in Fig. 3 a simple way to determine the distance which the traction wheel should be offset from the axis of the drive shaft in relation to the traction wheel radius is to give the traction wheel such a diameter, and offset it such an amount, that the point of contact of the gears 36 and 31, the point of intersection of the axes of the axle 39 and the drive shaft 28, and the point of contact of the traction wheel with the surface on which it rolls are in a straight line. When this conditicnris fulfilled, as shown in Fig. 3, W/L' (the ratio torch or other instrumentality at the saine linearspeed when the tracer is rounding a corner of` the pattern, as when it is moving along a straight` line vportion of the pattern.

f 4,Coming now to the question f objectionable steering torque produced by the Adriving ofthe traction wheel, it will bevseen from Fig. 3 thata driving force D at;the point of contact of the gearsc36 and 31 acts at a radius L to produce a steering torque DL which tends to turn the member in which the traction wheel is journalled and thereby tendsv to steer the traction f wheel as previouslyexplained in connection with Fig. 1. However, the Vsurface on which the traction wheel rolls provides a reactive force R Iacting at the radius L to produce a counter steering torque RL'.. Thus, when the traction wheel is positioned so that it is olset with respect to the axis of the drive shaft Vup to a certain limit the steering torque produced by the driving of the traction wheel is at least partly counteracted or nullied. Whenv the gearingis of the type shown in Fig. 3 the steering .torque is exactly counteracted or nullied so that it produces no bias on the automatic steering mechanism, when the traction wheel is oiset by a distance such that the ratio of the traction wheel radius to such distance is f oiiset distance L is. made equal to the overall reduction ratio ofjtheentire train voi" gears if the speeding up or slowing down of the traction wheel due to the planetary action of the Worm wheel 41 revolving around the worm 46Ywhen the sleeve 3| is turnedis to be completely ycompensated for in the manner previously described.

In other words, viiG represents the overall re-V duction ratio of the gears (drive shaft to trace tion wheel) W/L should equal G.

Moreover, .the steering torque produced by the drivingof the traction Wheel and which tends -to .turn rthe sleeve 3| about the axis'oi the drive shaft and thus steer the traction wheel isv corn,- pletely counteracted'or nulliedwhen the traction wheel is offset .in that manner, i. e..when

This can be proved as follows:

n Let'TiTorque'eXerted by drive motor on drive equal to the reduction ratio of the gearing; in

votherwords, when I Q L"L K in Fig. 3, as will be seen from the following: L=g=Reduction ratio of drive gearing,

and drive force DX AG=Reactive force RXW Q7 D Substituting: gigi L DL DL= RL' Since the steering,` torques are equal and opposite there is no net eiect tending to steer the traction wheel, and the other objection toprior art power-driven tracers is thus overcome.

The invention is applicable to any type of reduction gearing between the drive shaft and the traction wheel so long as the overall reduction ratio of the gear train is used in determining A the optimum amount thatjthetraction 1'wheel should be offset with respect to the axis of the drive shaft. Figs. 7 and 8 illustrate the invenftion` as applied to worm gearing of ka type frequently used in vpower-driven tracers. A worm 46 (Fig. 7) at the lower end ofthe driveshaft 2,8v meshes with a worm wheel 41' rotatably .mounted in a housing 48 secured to the lower end of therotatable sleeve 3f; The worm wheel 4l is secured to a spur gear 4S which meshes with a Aspurgear 50 secured t-o the traction Wheel 35. Figt `shows the traction wheel oiset with respect to the drive shaft 28 by a distance L'.- .The ratio of the radius W ofy the traction wheel to the shaft. `(Driving torquey as well ,as steering torque) p v i R=Reactive force of tracing table surface on traction wheel.

(1,) Y n=56 (2) Counter steering'torque=R L As above stated: f

sbstuitutingfm 'Equation 2:' f v Y `'Counter steering'.torqu-e%V but, v v

T1=1%V (Equation v1) y therefore, RLvT-i Hence, the steering torque (T1) is completely compensated for by; the kcounter steering torquep(RL')`. i I f Y While the invention `has been described las applied to a tracer, in its broader aspects, itais applicable to any self-propelled, deviceorap paratus, such as a carriage, having a steerable tractiongwheel =which is power-driven, in the manner hereinbefore described, where it is desired that the carriage, or the like, travel at the same rateof speed when turning corners Ias when travellingin a straight lin'e, or where it is desiredv that the driving o'f the tractionwheel f does not have an, lobjectionable iniluence on 'the steeringof the traction wheel.

As above shown the same amountioi offset of thetraction wheel is required to'compensate for tween the. drive shaft and thetraction' wheel if' `friction is neglected. l The theoretical amount of oiset of the .traction wheel required Ato'bring about exact compensation for the.; objectionable around the 'driving gear in a when-said member is rotated about the axis of 'the-drive shaft to steer ratio of said gearingll conditions can be deviated from somewhat,Y if desired, to compensate `for friction.

l.' Self-propelled steerable apparatus comprising a traction wheel; a member in which the traction wheel is rotatably mounted, a drive shaft fori-the tractionwheelfwhose axis intersects the axis-of rotation of the traction wheel, said 'member' being rotatable aboutthe q axis lof the drive shaftto steer the traction-wheel, power means -for rotating the ydrive shaft at a substantially constant speed, 'and reduction gearing between thedrive shaft and the `traction wheel, said traction wheel "being :positioned so that its point of contact with the Vsurface alone `which the" tracvtionwheel travelsis 'located toione side ofthe axis of the drive shaft. l i

2. Self-propelled steerable apparatus comprising a traction wheel, a member in which the traction wheel is rotatably mounted, a drive shaft f or r`the traction wheel whose `axis intersects the axis ofrotation of the traction wheel, said memberbeing rotatable aboutthe axis .of the drive ,Shaft to steer thetraction wheel, 1power means for rotating' the driveshaft ata substantially constant speed, and reduction gearingbetween the drive shaft and the traction wheel, said traction wheel beingv positioned so that its point of contact with the surface along which the traction wheel travels is locatedto one side of the axis of the drive shaft by a distance such that the ratio of the traction wheel radius to such distance is substantially equal to the reduction ratio of said gearing.

3. Self-propelled steerable apparatus comprising a traction wheel,A a member in which the traction wheel is rotatablymounted, a drive shaft for the traction Wheel whose axis intersects the axis of rotation of the, traction wheel, said member being rotatable' about shaft to steerthe traction wheel, power means for rotating the drive shaft at a substantially the axis of the drive i constant speed, and reduction gearing between y the drive shaft and the traction wheel including a driving gearyon. thedrivefshaft and a driven gear carried by said member which revolves around the driving gear in avplanetary fashion when said member is rotated about the axis of the drive-shaft to steer the: traction wheel, said traction wheelbeingpositioned so that its point of contact with the surface along whichV the tractionv wheel travels islocated to-one side of the axis of the drive shaft.

4,'Self-propelled steerable apparatus comprising la traction wheel, a member inV traction wheel isrotatably mounted, a-drive shaft for the traction wheel whose axis intersects the axis of rotation ofthe traction wheel, said mem- "berf being rotatable about the axis of they drive {shaft to for frotatingthe drive' shaft at' a substantially -l constant speed, and

the drive shaft andthe traction Wheel including la drivingwgear on thesteer the tractionwheel, vpower means reduction! gearing between drive shaft and a driven gear-carried by said member which revolves planetary fashion the traction wheel, said tractionl wheel being positioned so that itspoint of contact with the surface along which the trac- 'tion Iwheel travelsv is located to one side of the jaxis'of the drive shaft the ratio of the traction by a distance such that wheel radius to such distance is substantially equal to the reduction which the 5. In a tracer having a'traction wheel,a memberin Vwhich the traction wheel kis `rotatably mounted, a drive shaft for the traction wheel whose axis intersects lthe axis of rotation :of `the traction wheel, power means for rotatingthe drive shaft at a substantially constant speed', said member being rotatable about the axis of 'the drive shaft to steer the traction wheel so that 'a 'given point on the tracer can be made -to ltrace an arc of a circle, `and reduction gearing between the drive shaft vand-the traction wheelincluding a driving gear on the drive .shaft andadriven gear carriedby said member and which revolves around the driving gearwith a planetary action when said member is rotated to steer thetraction wheel and thereby speeds up or slows down the rotation ofthe traction Wheel depending upon the direction in which said member-is rotated, the improvement in which the traction wheel is positioned so that its point of fcontact with the surface along which -the wheel travels is -spaced to one side of the axis of the drive shaft whereby when said'member is rotated to steer the traction wheel the traction wheel is caused to travel "along an arc parallel to the arc followed bythe-axis of the drive shaft, the traction wheel being on that side of the axis of the drive shaft such that rotation of said member ina direction'thatlspeeds up the rotation of the traction wheel causes the traction wheel to travel in an arc whichv is outside the arc traced by the axis of the drive shaft and such that rotation of said member in a direction that slows down the rotation of the traction wheel causes the traction wheelto travel lin an arc which 'is inside the'arc traced by the axis of the drive shaft; and the distance that said point of Contact of the tractionwheel vis spaced to one side of the axis of the drive shaft being such in relation to the 'traction wheel radius that for a given angular rotation of said member in a direction Vopposite tothedirection of 'rotation of the drive shaft the arc in which the traction wheel travelsv isi longer than the arc traced by the axis of the drive shaft by an amount which compensates for the kspeeding 'up ofA the traction wheel by said planetary action of the gearing and for a given angular rotation of said member in the opposite direction the arc in which the traction wheel travels is shorter than the arc traced by the axis of the drive shaft by an amount which compensates for the slowing down of the traction wheel by said planetary action of the gearing whereby said point on the tracer will always be moved'by-the traction wheel-at a constant speed unaffected by said planetaryaction of the gearing when the traction wheel `is steered to cause said point on the tracerto `follow an arc.

6. In a self-propelled steerable apparatus having a traction wheel, a member in which the traction wheel is rotatably mounted, a drive shaft for the "tractionwheelwhose axis intersects the axis of rotation-of the traction'. wheel, said member Ybeing rotatableV about the axis of the drive vshaft to steerthe traction wheel, powerrmeans for rotating the drive shaft;y and Vreduction geardrive shaft .and the traction wheel including `a driving gear on the drivev shaft and a driven gear carried by said member and located laterally` ofthe driving gear wherebyrotation of the drive shaft to drive the traction wheel tends to produce undesired rotation of said member and hence undesired steering of the traction wheel, the improvement in which the traction wheel is positioned so that its point of contact with the"surface along which the traction wheel travels is located drive shaft.

7. In a self-propelled steerable apparatus havl to one side of the axis of the ,ing a traction wheel, a member in which the traction Wheel is rotatably mounted, a drive shaft for the traction wheel whose axis intersects the axis of rotation of the traction wheel, said member being rotatable about the axis of the drive shaft to steer the traction wheel,

said gearing.

8. In a tracer having a traction Wheel, a member in which the traction Wheel is rotatably mounted, a drive shaft for the traction wheel whose axis intersects the axis of rotation of the traction Wheel, said member being rotatable about the axis of the drive improvement in which the traction Wheel is positioned so that its point of contact with the surface along which the traction Wheel travels is 14 located to one side of the axis of the drive shaft by a distance such that the ratio of the traction wheel radius to such distance is substantially equal to the reduction ratio of said' gearing.

l0. In an electronic tracer for automatically tracing a pattern and having a traction wheel, a member in which the traction Wheel is rotatably mounted, a drivel shaft for the traction Wheel Whose axis intersects the axis of rotation of the tractionwlleel, said member being rotatable about the axis of the drive shaft to steer the traction Wheel, automatic steering means operatively connected to said member including a photo-electric NELSON E. ANDERSON.

REFERENCES CITED UNITED STATES VPATENTS Number Name Date 2,172,313. Young Sept. 5, 1939 2,261,644 Cockrell Nov. 4, 1941 2,331,337 Meyer Oct. l2, 1943 

